The authors regret that, upon careful review of data from our quality control (QC) and quality assurance (QA) program, we have determined that the Frog cell line reported in this manuscript (FH-1 and FH-2) was misidentified, and it was actually a different hemangiosarcoma cell line called Dal-4. The Frog cell line was established in 2005 from a hemangiosarcoma of the spleen obtained from a 10-year old, female Golden Retriever. The Dal-4 cell line was established in 2000 from a hemangiosarcoma of the spleen obtained from a 7-year old, male Dalmatian. We believe that the conclusions from the paper are not affected by the breed, age, or sex of origin of the dog from which the tumours were obtained to establish the cell lines. The authors would like to apologise for any inconvenience caused.